PDF 320KB - Garry Oak Ecosystems Recovery Team

DETECTING CHANGES IN GARRY OAK
VEGETATION PLOTS AFTER 4 DECADES:
FOLLOWING IN DR. HANS ROEMER’S FOOTSTEPS
Jenny McCune
University of British Columbia
In order to understand how plant communities are changing in
response to human disturbance, it is useful to have a historical
baseline by which to measure changes. However, such baseline data
are often unavailable for many regions and time periods. On the
Saanich peninsula of Vancouver Island, Dr. Hans Roemer surveyed
over four hundred 20m by 20m relevé plots in the late 1960s as part
of his doctoral research. This provides a unique opportunity to
quantify the changes in vegetation on the Peninsula in the past 40
years. I used Dr. Roemer’s field notes to return to 184 of his plot
locations, 43 of which were in Garry oak communities, and
resurveyed them using the same methodology. Preliminary analyses
show that herbaceous plant richness in Garry Oak plots increased
significantly, from an average of 28.4 species to an average of 33.1
species. The total number of herbaceous species found in Garry Oak
plots increased from 121 in 1968 to 139 in 2009. Exotic species
represented approximately 20% of Garry Oak herbaceous flora in
1968, increasing to 40% by 2009. I looked for changes in plant
community composition by using Non-Metric Multidimensional
Scaling to ordinate all plots in both years. There seems to have been a
much larger shift in herbaceous plant composition in Douglas-firdominated
communities compared to Garry oak-dominated plots. I
hypothesize that this greater change in Douglas-fir-dominated
herbaceous flora may be due to a larger degree of fragmentation of
Douglas-fir forests between 1968 and 2009, whereas many Garry oak
plots were located in fragments that have not changed in size since
Dr. Roemer’s survey. Future work will aim to determine the
relationship between vegetation changes and changes in the degree of
human disturbance across the landscape. Using historical data is a
valuable way to gain understanding of vegetation changes, and
researchers today should consider making and keeping detailed notes
on the locations and methodology of their projects in order to provide
a baseline for ecologists of the future.
Garry Oak Ecosystems Recovery Team – Research Colloquium 2010 Page 19